Many toxic or environmentally unacceptable accumulations in underground locations are treated, removed, or otherwise remediated using underground conduits or wells. The wells are used to either inject materials, such as oxygen in a bioremediation process, or withdraw unwanted or contaminated materials, such as gasoline which has leaked from an underground tank.
Operating injection and withdrawal wells consumes energy, typically in the form of electricity to drive fluid pumps. If remediation requires long term operation, large amounts of energy are required, especially when a significant vacuum or pressure differential, e.g., more than 0.5 atmosphere, is required for remediating a large underground aquifer.
Injection wells typically provide a fluid path to a relatively shallow aquifer (when compared to other wells), e.g., the top of a contaminated groundwater aquifer being less than 20 feet (6.096 meters) below a "vadose" zone. If air is injected into the contaminated groundwater, air pressure must be increased above the aquifer pressure, e.g., injection pressure must be raised above the hydrostatic pressure of the ground water. The injected air tends to affect a zone of influence around the well and migrate upward because of water-air density differences.
Injection of air into a saturated zone of an aquifer (air sparging) with the intent of stripping dissolved volatile contaminants has become a commonly advocated alternative to conventional pump and treat systems (e.g., Brown and Jasiulewicz, 1992; Marley et al., 1992; and Leonard and Brown, 1993). Field tests have demonstrated that air sparging can, under the proper conditions, enhance the recovery of some contaminants through a combination of effects, including contaminant partitioning into the vapor phase and acceleration of bacterial degradation of contaminants by increasing dissolved oxygen concentrations. The primary advantages offered by air sparging are that surface water treatment equipment and water disposal may be eliminated, and that the remediation of sorbed contaminants is hopefully accelerated.
To most effectively implement air sparging, it is necessary to predict the pattern of air flow that will occur in the subsurface formation in order to determine the optimal placement and number of sparge wells and their operating conditions. It is desirable to operate sparge wells in such a way as to maximize the spatial extent of air flow regardless of whether volatilization or enhanced biodegradation is the primary remedial process. Withdrawal wells may withdraw liquid (e.g., spilled diesel fluid) or gases (e.g., hydrocarbon vapors). A downhole pump or vacuum is typically required to withdraw these fluids. Several wells (each drawing from a zone of influence around each well) may be required to remove the unwanted fluid to the surface.